Improvement of electrical resistivity tomography for leachate injection monitoring

Leachate recirculation is a key process in the scope of operating municipal waste landfills as bioreactors, which aims to increase the moisture content to optimize the biodegradation in landfills. Given that liquid flows exhibit a complex behaviour in very heterogeneous porous media, in situ monitoring methods are required. Surface time-lapse electrical resistivity tomography (ERT) is usually proposed. Using numerical modelling with typical 2D and 3D injection plume patterns and 2D and 3D inversion codes, we show that wrong changes of resistivity can be calculated at depth if standard parameters are used for time-lapse ERT inversion. Major artefacts typically exhibit significant increases of resistivity (more than +30%) which can be misinterpreted as gas migration within the waste. In order to eliminate these artefacts, we tested an advanced time-lapse ERT procedure that includes (i) two advanced inversion tools and (ii) two alternative array geometries. The first advanced tool uses invariant regions in the model. The second advanced tool uses an inversion with a “minimum length” constraint. The alternative arrays focus on (i) a pole–dipole array (2D case), and (ii) a star array (3D case). The results show that these two advanced inversion tools and the two alternative arrays remove almost completely the artefacts within +/?5% both for 2D and 3D situations. As a field application, time-lapse ERT is applied using the star array during a 3D leachate injection in a non-hazardous municipal waste landfill. To evaluate the robustness of the two advanced tools, a synthetic model including both true decrease and increase of resistivity is built. The advanced time-lapse ERT procedure eliminates unwanted artefacts, while keeping a satisfactory image of true resistivity variations. This study demonstrates that significant and robust improvements can be obtained for time-lapse ERT monitoring of leachate recirculation in waste landfills.     

Co-digestion of sewage sludge with glycerol to boost biogas production

The feasibility of adding crude glycerol from the biodiesel industry to the anaerobic digesters treating sewage sludge in wastewater treatment plants was studied in both batch and continuous experiments at 35 °C. Glycerol addition can boost biogas yields, if it does not exceed a limiting 1% (v/v) concentration in the feed. Any further increase of glycerol causes a high imbalance in the anaerobic digestion process. The reactor treating the sewage sludge produced 1106 ± 36 ml CH₄/d before the addition of glycerol and 2353 ± 94 ml CH₄/d after the addition of glycerol (1% v/v in the feed). The extra glycerol-COD added to the feed did not have a negative effect on reactor performance, but seemed to increase the active biomass (volatile solids) concentration in the system. Batch kinetic experiments showed that the maximum specific utilization rate (μ_max) and the saturation constant (K_S) of glycerol were 0.149 ± 0.015 h^?1 and 0.276 ± 0.095 g/l, respectively. Comparing the estimated values with the kinetics constants for propionate reported in the literature, it can be concluded that glycerol uptake is not the rate-limiting step during the process.     

Stream Restoration and Enhancement Projects: Is Anyone Monitoring?

Declines in salmon stocks and general watershed health in Washington State, USA, have led to an increase in stream restoration and enhancement projects initiated throughout the state. The increasing number of projects has also raised questions regarding the monitoring of these efforts. Project managers receiving hydraulic project approvals (HPAs) were surveyed to determine whether monitoring was taking place on their projects. About half the project managers surveyed reported the collection of baseline data and the use of biological, physical, chemical, or other water quality measures for their projects. Of those who reported collection of monitoring data, only 18% indicated that monitoring was required. Respondents were also asked to rank the importance of various project goals on a Likert scale. Project managers with projects focusing on “engineering” goals (e.g., roadbed stabilization) were less likely than other project managers to collect baseline monitoring data. Project managers with projects focusing on “restoration/ecological” or “fisheries” goals were more likely than other project managers to collect monitoring measures. Although monitoring appears to be taking place in slightly more than half of the projects surveyed, the nature of the data collected varies widely across projects, and in most cases the monitoring effort is voluntary. This suggests that project sponsors, funders, and managers must consider the issues involved in requiring appropriate monitoring, establishing standardized monitoring guidelines, the time frames in which to monitor, providing other incentives for conducting monitoring, and ensuring adequate funding for monitoring efforts.     

Comparison among model estimates of critical loads of acidic deposition using different sources and scales of input data

The critical load (CL) of acidic atmospheric deposition represents the load of acidity deposited from the atmosphere to the earth’s surface at which harmful acidification effects on sensitive biological receptors are thought to occur. In this study, the CL for forest soils was estimated for 27 watersheds throughout the United States using a steady-state mass balance approach based on both national and site-specific data and using different approaches for estimating base cation weathering. Results suggested that the scale and source of input data can have large effects on the calculated CL and that the most important parameter in the steady-state model used to estimate CL is base cation weathering. These results suggest that the data and approach used to estimate weathering must be robust if the calculated CL is to be useful for its intended purpose.     

Review of Russian language studies on radionuclide behaviour in agricultural animals: 3. Transfer to muscle

Over 150 publications reporting studies conducted in the former USSR were reviewed to provide transfer coefficients (F_f) to the muscle of domestic animals from experiments using chronic administration, often for long timescales in large scale experiments. Only a few of these studies were made available in the English language literature or taken into account in international reviews. The values derived have been compared with expected values reported by the IAEA's Handbook of parameter values for the prediction of radionuclide transfer in temperate environments (TRS 364) where possible. The information presented here has been used in the current updating of parameters recommended for environmental assessments by the IAEA. Many of the reported values are for Sr due to the Mayak accident and Cs due to the Chernobyl accident. Nevertheless, the reported data for a wide range of radionuclides, in particular for Ru, Sb, and Zn markedly improve the extent of available data.     

The food-print of Paris: long-term reconstruction of the nitrogen flows imported into the city from its rural hinterland

Between the tenth and twentieth century the population of Paris city increased from a few thousand to near 10 million inhabitants. In response to the growing urban demand during this period, the agrarian systems of the surrounding rural areas tremendously increased their potential for commercial export of agricultural products, made possible by a surplus of agricultural production over local consumption by humans and livestock in these areas. Expressed in terms of nitrogen, the potential for export increased from about 60 kg N/km2/year of rural territory in the Middle Ages, to more than 5,000 kg N/km2/year from modern agriculture. As a result of the balance between urban population growth and rural productivity, the rural area required to supply Paris (i.e. its food-print) did not change substantially for several centuries, remaining at the size of the Seine watershed surrounding the city (around 60,000 km2). The theoretical estimate of the size of the supplying hinterland at the end of the eighteenth century is confirmed by the figures deduced from the analysis of the historical city toll data (octroi). During the second half of the twentieth century, the ‘food-print’ of Paris reduced in size, owing to an unprecedented increase in the potential for commercial export associated with modern agricultural systems based on chemical N fertilization. We argue that analysing the capacity of territories to satisfy the demand for nitrogen-containing food products of local or distant urban population and markets might provide new and useful insights when assessing world food resource allocation in the context of increasing population and urbanization.     

Methanotrophs and methanotrophic activity in engineered landfill biocovers

The dynamics and changes in the potential activity and community structure of methanotrophs in landfill covers, as a function of time and depth were investigated. A passive methane oxidation biocover (PMOB-1) was constructed in St-Nicéphore MSW Landfill (Quebec, Canada). The most probable number (MPN) method was used for methanotroph counts, methanotrophic diversity was assessed using denaturing gradient gel electrophoresis (DGGE) fingerprinting of the pmoA gene and the potential CH₄ oxidation rate was determined using soil microcosms. Results of the PMOB-1 were compared with those obtained for the existing landfill cover (silty clay) or a reference soil (RS). During the monitoring period, changes in the number of methanotrophic bacteria in the PMOB-1 exhibited different developmental phases and significant variations with depth. In comparison, no observable changes over time occurred in the number of methanotrophs in the RS. The maximum counts measured in the uppermost layer was 1.5 × 10⁹ cells g dw^?1 for the PMOB-1 and 1.6 × 10⁸ cells g dw^?1 for the RS. No distinct difference was observed in the methanotroph diversity in the PMOB-1 or RS. As expected, the potential methane oxidation rate was higher in the PMOB-1 than in the RS. The maximum potential rates were 441.1 and 76.0 μg CH₄ h^?1g dw^?1 in the PMOB and RS, respectively. From these results, the PMOB was found to be a good technology to enhance methane oxidation, as its performance was clearly better than the starting soil that was present in the landfill site.     

Fractions and background concentrations of potentially toxic elements in Hungarian surface soils

This work established background concentrations for the pseudo total (HNO₃ + H₂O₂-soluble), mobilisable (NH₄-acetate + EDTA-soluble) and mobile (1?M NH₄NO₃-soluble) element fractions of Hungarian surface soils that can be used as reference values for the soil quality standards. The 193 soils investigated were taken from the Hungarian Soil Information and Monitoring System. The background values for Al, As, B, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sr and Zn were given as a range covering 95% of the variance of the representative samples. The differences between observed element concentrations and the calculated background values indicated anthropogenic or pedogenic impact in each fraction. The comparison of the calculated background values with the Hungarian quality standards and the contamination limit values of other countries showed that the limit values of a certain region or country are not suitable for other areas. Generally, Mn and Al had the highest, while Cd had the lowest concentration in each fraction. Cr and Al were the least and Sr was the most mobile element. The principal component analysis indicated different geochemical and physico-chemical behaviour of the elements in the fractions; the pseudo total fraction was influenced more by the geological behaviour, while mobilisable and mobile fraction explained a much higher proportion of the total variance of soil physico-chemical properties than soil geochemical properties. The Cd–Ni and Co–Mn element pairs were always in the same principal component in each fractions indicating similar geogenic origin and showing that their solubility changes are similar in function of soil properties.     

Composting projects under the Clean Development Mechanism: sustainable contribution to mitigate climate change

The Clean Development Mechanism (CDM) of the Kyoto Protocol aims to reduce greenhouse gas emissions in developing countries and at the same time to assist these countries in sustainable development. While composting as a suitable mitigation option in the waste sector can clearly contribute to the former goal there are indications that high rents can also be achieved regarding the latter. In this article composting is compared with other CDM project types inside and outside the waste sector with regards to both project numbers and contribution to sustainable development. It is found that, despite the high number of waste projects, composting is underrepresented and a major reason for this fact is identified. Based on a multi-criteria analysis it is shown that composting has a higher potential for contribution to sustainable development than most other best in class projects. As these contributions can only be assured if certain requirements are followed, eight key obligations are presented.